Solid phase extraction (SPE) is a chromatographic technique that is widely used, e.g., for preconcentration and cleanup of analytical samples, for purification of various chemicals, and for removal of toxic or valuable substances from aqueous solutions. SPE is usually performed using a column or cartridge containing an appropriate material or sorbent. SPE procedures have been developed using sorbents that can interact with analytes by hydrophobic, ion-exchange, chelation, sorption, and other mechanisms, to bind and remove the analytes from fluids.
Because different SPE applications can require different sorbents, there is a need for sorbents with novel properties that have unique selectivities. These include superior wetting characteristics, selective capture of analytes of interest, and non-retention of interfering analytes. Sorbents comprising porous particles having the aforementioned properties are described in WO 99/64480 and in U.S. Pat. No. 6,322,695B1.
However, a problem associated with porous particles is the passage or leaching of particles through the retaining frit of the separation device into the sample of interest. In addition to contamination of the sample, the passed particles can further negatively impact test methods and the HPLC systems that are used to test the samples. For example, the particles may clog or block in line filters or column frits which in turn lead to high system backpressures and ultimately HPLC pump shutdown.
Monolith materials have been developed in an attempt to overcome the problem of particle passage or leaching through frits. These include polymeric monoliths such as polymethacrylate monoliths (U.S. Pat. No. 5,453,185, U.S. Pat. No. 5,728,457); polystyrene-DVB monoliths (U.S. Pat. No. 4,889,632, U.S. Pat. No. 4,923,610, U.S. Pat. No. 4,952,349); charge incorporated polymethacrylate monoliths for the application of reversed-phase ion-pairing chromatography (U.S. Pat. No. 6,238,565); monoliths based on ROMP metathesis (WO 00073782); and (EP 852334) continuous monolith columns made from water-soluble polymerizable monomers, such as vinyl, allyl, acrylic and methacrylic compounds, without porogens but in the presence of high concentration of inorganic salts such as ammonium sulfate.
Polymeric monoliths are chemically stable against strongly alkaline and strongly acidic mobile phases, allowing flexibility in the choice of mobile phase pH. However, the prior art monoliths do not necessarily provide the unique selectivities and advantages that are needed for a variety of chromatographic applications, in particular SPE applications.